This Project investigates one of the most important ways in which humans learn to make sound decisions: through observing other people. Whereas Project 1 investigated how we value social and nonsocial stimuli (social reward processing), this Project 2 investigates how we learn from other people about rewards (observational learning). Do the same computations of decision values and experienced values that were investigated under Project 1 also come into play when we watch others? If so, do they recruit the same brain structures? Four Specific Aims systematically investigate how the mechanisms behind observational learning might contrast with the much better studied mechanisms behind learning from direct experience. The first Aim focuses on a structure thought to encode reward prediction errors in dopaminergic neurons that drive learning, the ventral striatum, and recordings in monkeys. The second Aim extends these studies to humans, using single-unit and LFP data from intracranial recordings, together with fMRI and focuses on the target structures of dopamine projections: amygdala and vmPFC. The third Aim asks what difference it might make exactly who we are observing: whether the person is competent or not, whether they are a friend or a stranger; this Aim looks at such modulation in the ventral striatum, the amygdala, and the ventromedial prefrontal cortex. The fourth Aim explores possible individual differences between the fMRI data obtained under Aims 1 and 2, and the psychological variables assessed under Core 3.